1. Field of the Invention
This invention relates to a cooling device for overhead type slide projectors, and more particularly to a cooling device which can cool transparencies being projected by overhead type slide projectors.
2. Description of the Prior Art
In the case of the so-called horizontal type slide projectors having condenser lenses and light-source lamps disposed on one level with a horizontal spacing therebetween, it has been a general practice to dispose a blowing fan on a plane where the lens system of the projector lies, so as to produce horizontal air flow for simultaneously cooling transparencies, condenser lenses, and the light-source lamp.
On the other hand, in the case of a widely used overhead type slide projector, a second condenser lens and transparencies are disposed above a translucent diffusing plate mounted on an upper portion of a framework of the projector. If such overhead type slide projector is cooled by the above-mentioned cooling device of the horizontal type slide projectors, the second condenser lens and the transparencies cannot be cooled suffficiently. Besides, when a halogen lamp is used as a light-source lamp, if the halogen lamp is cooled to the same level as that of the transparencies, the lamp may be cooled to a temperature below a desired point and the active halogen regenerating cycle may be hampered.
To solve the above-mentioned difficulties, the inventor disclosed in his Japanese Pat. No. 967883 a cooling device for overhead type slide projectors, which cooling device comprises a lens-holder member mounted on an upper portion of a lamp house so as to hold a second condenser lens at a level corresponding to the upper end of the lamp house, a translucent diffusing plate closing the top end of the projector framework, said lens-holder member having a top edge thereof extending upwards through said translucent diffusing plate so as to reach the proximity of that position where a transparency is to be held during projection, sucking holes formed between said lens-holder member and said second condenser lens, and a sucking fan disposed at one side of the lamp house in such a manner that the intake side of the sucking fan communicates with said sucking holes through the inside of said lamp house.
To facilitate storage of a number of transparencies in an orderly manner, the inventor has also disclosed a slide-filing sheet in his Japanese Pat. No. 1055825, which slide-filing sheet removably holds a plurality of transparencies, such as regular photographic slides for microscopic inspection, in a matrix arrangement in one plane. The disclosed slide-filing sheet holds the transparencies, such as those mounted on slide frames, parallel to but spaced from the bottom wall thereof. An air inlet opening and an air outlet opening are provided for each of the spaces between the transparencies and the bottom wall of the slide-filing sheet, so that air from the air inlet opening flows through both said space and said air outlet opening, so as to prevent the transparencies from being damaged by heating.
However, it is difficult to keep the transparencies carried by the slide-filing sheet at a temperature below about 60.degree. C. during projection, even if the last-mentioned cooling device of the inventor is used. Thus, the prior art device for overhead type slide projectors has a shortcoming in that it cannot prevent discolouring and bending of transparencies after projection for a certain length of time.